Constant true strain rate (2 s$ sp{-1})$ compression tests with one or two interruptions were carried out on a series of steels over the temperature range 900-1050$ sp circ$C. Based on a 0.07% C, 1.25% Mn and 0.006% N reference steel, the three microalloyed steels contained the following: (i) 0.08% Al, (ii) 0.04% Nb, or (iii) 0.045% Nb and 0.08% Al. The degree of fractional softening during the interpass was used to assess recrystallization start (R$ sb{ rm s})$ and finish (R$ sb{ rm f})$ times as well as those for the onset (P$ sb{ rm s})$ and termination (P$ sb{ rm f})$ of precipitation. / Relative to a plain C steel, the static recrystallization kinetics show that the single solute retarding effect of Al is small but measurable while that of Nb is substantially larger. The influence of each element is enhanced when they are present jointly. The retardation effects observed at 1000$ sp circ$C are due solely to the presence of these elements in solution. Additional delays observed at or below 950$ sp circ$C in the two Nb bearing steels are ascribed to strain induced precipitation of Nb(CN). / The P$ sb{ rm s}$ times were estimated from the fractional softening data as well as from stress relaxation type tests. The presence of high levels of Al retarded the onset of Nb(CN) precipitation while it accelerated its progress. The Nb precipitates were cube shaped and heterogeneously distributed, suggesting that they were formed on dislocation networks. / A thermodynamic model was developed for the alloy system studied. The calculations indicated that there is a higher chemical driving force for precipitation in the Nb steel than in the Nb-Al steel at a given temperature. Consequently, this produces a higher equilibrium mole fraction of Nb(CN) in the former. The P$ sb{ rm s}$ times calculated based on the classical nucleation theory are in good agreement with the values observed. / Three hit test results further showed that increased hold times between the first two hits decrease the rate of softening between the second and third hits. Residual strain in the partially recrystallized structure is more effectively accumulated at lower temperature due to slower softening rates. These data enabled the development of a model for calculation of residual strains following a hold in a partially recrystallized structure. (Abstract shortened by UMI.)
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.74566 |
| Date | January 1990 |
| Creators | Wang, Ganlin |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Department of Mining and Metallurgical Engineering.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001168043, proquestno: AAINN66485, Theses scanned by UMI/ProQuest. |
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